458 Scientific Intelligence. 



of nature might be merged into the spacial relations. The five 

 succeeding chapters discuss some of the consequences of the theory 

 and their experimental investigation. The twelfth and final 

 chapter gives some of the author's speculations upon the nature of 

 things which seem to be summed up in the concluding paragraph 

 which reads : ' ' We have found a strange foot-print on the shores 

 of the unknown!. We have devised profound theories one after 

 the other to account for its origin. At last we have succeeded in 

 reconstructing the creature that made the foot-print. And Lo! 

 it is our own." 



The book will give the reader a good idea of the Einstein 

 theory and how it has led to the prediction of three exceedingly 

 minute quantities, namely, the secular motion of the perihelion 

 of Mercury, the deviation of ray of light passing close to the sun, 

 and the change in frequency of radiation in an intense gravita- 

 tional field, for all of which evidence is now supposed to have 

 been found. On the other hand the book seems, at least to ojie 

 reader, too dogmatic in its presumption that the physical world 

 is but the stuff of our consciousness and that physical phenomena 

 are due to the oddities of space. The attitude of the physicist in 

 general is a little more tolerant. He is content to specify such 

 postulates or abstractions from the complex world of reality as 

 are sufficient for the set of problems in hand and later if experi- 

 ment shows that these are too limited he is frankly willing to 

 extend them. For example, the ordinary problems of hydro- 

 dynamics are well enough discussed on the assumption of a con- 

 tinuum, but he does not feel that he must be held to this assump- 

 tion when treating of the chemical properties of water or of the 

 radiations from the hydrogen atom. Similarly if it should 

 appear that time does not run on at a uniform rate, or that it is 

 desirable to assume that it is discrete in structure, possessing 

 something like the quantum in energy, doubtless the physicist will 

 be ready to adopt the new hypoth-^sis, only he will insist that it 

 corresponds to something real in nature. 



While there is no doubt that the interlacing of space and time 

 into a differential quadratic affords a valuable technique for the 

 solution of problems in electrodynamics, the question whether a 

 whole philosoph}^ of nature based on an absolute velocity, as of 

 light, will win universal acceptance, must still be considered an 

 open one. 



The reader who may care for a more open-minded discussion 

 of the subject will be interested to read the article on Gravitation 

 and Light by Sir Joseph Larmor in the Proceedings of the Cam- 

 bridge Philosophical Society, 19, 324, 1920. f. e. b. 



9. The Principle of Relativity ; by H. Wildon Carr. Pp. 

 \i\, 163. London, 1920 (MacmiUan and Co.).— This little book 

 on the philosophical aspects of relativity is the outcome of a 

 course of lectures on ''Historical Theories of Space, Time and 

 Movement" delivered by the author at Kings College last year. 



